The onsemi HCPL0639 is a dual-channel optoisolator in an 8-SOIC package, rated for 10 Mbps data rate and 3750 Vrms isolation. This combination suits it for isolating digital communication lines — think SPI, UART, or CAN bus isolation — where you need to break ground loops without slowing the link below the bus speed. The 25 kV/µs common-mode transient immunity means the part holds its output state when a fast voltage transient slams across the isolation barrier — a motor drive or inverter with IGBT switching edges in the tens of kV/µs range is exactly the environment where this matters. Without that rating, the output glitches and the downstream logic sees a false pulse.
Output stage and timing — open collector with Schottky clamp
The output is an open collector with a Schottky clamp, rated for 15 mA per channel. The Schottky diode across the output transistor prevents saturation, which cuts the propagation delay to 75 ns max and the fall time to 5 ns typical — the output pulls low fast, keeping the bit period clean at 10 Mbps. Rise time is 17 ns typical, so the output edge into a standard CMOS load is well within the timing budget for a 10 Mbps line.
The 8-SOIC footprint (3.90 mm width) is a standard surface-mount package; the same board layout accepts the single-channel HCPL0600 or the quad-channel HCPL0661 if the channel count changes in a later BOM revision. Forward voltage is 1.75 V max at the LED input — a 5 V logic output drives it directly through a series resistor sized for the target forward current. The DC input type means it accepts a steady-state logic level, not an AC-coupled signal.